A global climate modeling study of Antarctic cloud radiative processes

Simulations with the National Center for Atmospheric Research (NCAR) Community Climate Model version 3 (CCM3) are performed to detail the impact of Antarctic clouds on the global climate. For improved simulations of polar clouds and radiative processes, both the prognostic cloud particulate scheme of Rasch and Kristjansson and the Rapid Radiative Transfer Model (RRTM) developed by Atmospheric and Environmental Research (Inc.) have been implemented in a version of CCM3. This version of CCM3 simulates a much improved pattern of sea level pressure near Antarctica compared to earlier simulations with the NCAR CCM2. In the CCM3 simulations, the intensity of the Antarctic circumpolar trough is reduced and much closer to observed values. Additionally, the positioning of troughs and ridges over the Southern Ocean are more realistic. Biases, however, still remain in the simulated polar radiation budget. Consequently the polar tropospheric temperatures are too cold and the middle-tropospheric circumpolar vortex is too strong. The semiannual wave in high southern latitudes is still not properly simulated. The circumpolar trough has a sharp pressure maximum during January and a flat minimum during winter.Improvements to the radiative processes of Antarctic clouds are also tested with 15-year sensitivity experiments.